Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The description confirms the mutating nature of the tool ('add or overwrite') consistent with readOnlyHint=false. It adds context that operations apply to an 'existing session', but does not disclose side effects beyond overwriting, nor permissions or error scenarios. Annotations already cover basic behavioral traits.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, efficient sentence with no extraneous information. Every word is necessary to convey the core action and context.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's complexity (mutation with nested object parameter, no output schema), the description is too brief. It omits important details like return value, error behavior when the session does not exist, and a fuller explanation of the entries structure. The high number of sibling tools also demands more context for differentiation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 50% (only entries has a description). The description adds minimal value by mentioning 'named entries', but does not explain the sessionId parameter or clarify the entries format beyond the schema's example. It insufficiently compensates for the missing schema description.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description uses a specific verb ('Add or overwrite') and resource ('named entries in an existing session'), making the tool's purpose clear. It distinguishes from sibling tools like session_create, session_get, and session_run by focusing on writing to an existing session.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides no guidance on when to use this tool versus alternatives, such as session_create or session_run. It does not mention prerequisites (session must exist) or situations where this tool should not be used.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.